| 摘要 |
PROBLEM TO BE SOLVED: To provide an optical system that can manufacture, at low cost, a plurality of optical systems that differ in the observation range of an approximately lateral object side, and enables simultaneous observations of front and approximately lateral objects. SOLUTION: The optical system comprises, in order from a front-object side: a front group Gf which has a reflective refractive optical element and has negative refractive power, an aperture stop S; and a rear group Gr which has positive refractive. The reflective refractive optical element is formed by cementing a first lens and a second lens located on the image side of the first lens. The reflective refractive optical element includes: a first surface, which has a first transmitting surface and a first reflective surface circularly formed around the first transmitting surface to be faced toward an image side, and which is formed on the front-object side of the first lens; a second surface, which has a second transmitting surface and a second reflective surface circularly formed around the second transmitting surface to be faced toward the front-object side, and which is formed on the cemented surfaces of the first and second lenses ; a third surface, which is formed as a transmitting surface on the image side of the second lens; and a fourth surface, which is formed as a transmitting surface on the periphery of the first lens. COPYRIGHT: (C)2011,JPO&INPIT
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